U.S. patent application number 12/524571 was filed with the patent office on 2010-02-11 for transvascular nerve stimulation apparatus and methods.
This patent application is currently assigned to SIMON FRASER UNIVERSITY. Invention is credited to Joaquin Andres Hoffer.
Application Number | 20100036451 12/524571 |
Document ID | / |
Family ID | 39673597 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100036451 |
Kind Code |
A1 |
Hoffer; Joaquin Andres |
February 11, 2010 |
TRANSVASCULAR NERVE STIMULATION APPARATUS AND METHODS
Abstract
Electrode structures for transvascular nerve stimulation combine
electrodes with an electrically-insulating backing layer. The
backing layer increases the electrical impedance of electrical
paths through blood in a lumen of a blood vessel and consequently
increases the flow of electrical current through surrounding
tissues. The electrode structures may be applied to stimulate
nerves such as the phrenic, vagus, trigeminal, obturator or other
nerves.
Inventors: |
Hoffer; Joaquin Andres;
(Anmore, CA) |
Correspondence
Address: |
OYEN, WIGGS, GREEN & MUTALA LLP;480 - THE STATION
601 WEST CORDOVA STREET
VANCOUVER
BC
V6B 1G1
CA
|
Assignee: |
SIMON FRASER UNIVERSITY
Burnaby
BC
|
Family ID: |
39673597 |
Appl. No.: |
12/524571 |
Filed: |
January 29, 2008 |
PCT Filed: |
January 29, 2008 |
PCT NO: |
PCT/CA2008/000179 |
371 Date: |
July 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60887031 |
Jan 29, 2007 |
|
|
|
Current U.S.
Class: |
607/42 ; 600/364;
607/116; 607/2; 607/62 |
Current CPC
Class: |
A61N 1/3601 20130101;
A61N 1/05 20130101; A61N 1/0558 20130101; A61N 1/3611 20130101;
A61N 1/36185 20130101; A61N 1/36139 20130101; A61N 1/0551
20130101 |
Class at
Publication: |
607/42 ; 607/116;
600/364; 607/62; 607/2 |
International
Class: |
A61N 1/372 20060101
A61N001/372; A61N 1/05 20060101 A61N001/05; A61B 5/145 20060101
A61B005/145; A61N 1/36 20060101 A61N001/36; A61F 2/86 20060101
A61F002/86 |
Claims
1. An electrode structure for use in transvascular nerve
stimulation, the electrode structure comprising: an electrode
supported on an electrically-insulating backing sheet; and, a
structure for holding a first major face of the backing sheet
against the inner wall of a blood vessel with the electrode in
contact with the inner wall of the blood vessel.
2. An electrode structure according to claim 1 wherein the holding
structure comprises an expandable stent.
3. An electrode structure according to claim 1 wherein the stent
comprises an expandable metal wire stent.
4. An electrode structure according to claim 2 wherein the stent is
affixed to the backing sheet.
5. An electrode structure according to claim 4 wherein the stent is
affixed to the backing sheet along a line extending generally
parallel to a longitudinal bore of the stent.
6. An electrode structure according to claim 4 wherein, the backing
sheet is dimensioned to extend around an outer circumference of the
stent when the stent is in an expanded configuration.
7. An electrode structure according to claim 2 wherein the backing
sheet is rolled to provide a bore and the structure comprises an
inflatable balloon removably disposed in the bore.
8. An electrode structure according to claim 2 wherein the backing
sheet is rolled to form a bore and the holding structure comprises
the backing sheet biased to unroll against the inner wall of the
blood vessel.
9. An electrode structure according to claim 1 wherein the holding
structure comprises means for engaging a first edge portion on a
first major face of the backing sheet with an opposing second edge
portion on a second major face of the backing sheet, the second
major face opposing the first major face.
10. An electrode structure according to claim 9 wherein the means
for engaging comprises a first plurality of ridges extending along
the first edge portion and a second plurality of ridges extending
along the second edge portion.
11. An electrode structure according to claim 10 comprising a tab
projecting out of a plane of the backing sheet on the first major
face adjacent the second edge portion.
12. An electrode structure according to claim 1 comprising a
plurality of electrodes spaced apart across a width of the backing
sheet.
13. An electrode structure according to claim 12 rolled inside an
insertion tube wherein the insertion tube is apertured and at least
one of the electrodes is exposed through an aperture in the
insertion tube.
14. An electrode structure according to claim 12 comprising a ridge
extending between two adjacent ones of the electrodes, the ridge
projecting from a major surface of the backing sheet.
15. An electrode structure according to claim 1 wherein the
electrode has a face that is curved to generally match a curvature
of an inner wall of a blood vessel.
16. An electrode structure according to claim 1 comprising a
plurality of electrodes arranged in a two-dimensional array on a
first major surface of the backing sheet.
17. An electrode structure according to claim 16 wherein the
backing sheet is pre-formed with a curvature such that the first
major surface has a convex cylindrical curvature.
18. An electrode structure according to claim 17 wherein the
electrodes have contact surfaces curved about an axis that is
parallel to an axis of curvature of the first major surface.
19. An electrode structure according to claim 1 comprising a blood
chemistry sensor.
20. An electrode structure according to claim 19 wherein the blood
chemistry sensor comprises a blood oxygen sensor.
21. An electrode structure according to claim 19 wherein the blood
chemistry sensor comprises a blood CO2 sensor.
22. A nerve stimulation system comprising an electrode structure
according to claim 1 connected to a stimulation signal
generator.
23. A nerve stimulation system according to claim 22 wherein the
stimulation signal generator comprises an implantable pulse
generator.
24. A nerve stimulation system comprising an electrode structure
according to claim 22 wherein the stimulation signal generator is
configured to regulate the generation of stimulation signals in
response to a signal from a sensor.
25. A nerve stimulation system according to claim 24 wherein the
sensor comprises an accelerometer.
26. A nerve stimulation system according to claim 24 wherein the
sensor comprises a blood chemistry sensor.
27. A nerve stimulation system according to claim 26 wherein the
blood chemistry sensor is co-located with the electrode
structure.
28. A nerve stimulation system according to claim 22 wherein the
electrode structure is one of a plurality of electrode structures
and the stimulation signal generator is configured to coordinate
the delivery of stimulation signals to electrodes of each of the
plurality of electrode structures.
29. A nerve stimulation system according to claim 25 wherein the
stimulation signal generator is configured to cause simultaneous
delivery of stimulation signals to the electrodes of each of the
plurality of electrode structures.
30. Use of an electrode structure according to claim 1 for
stimulating a nerve in a mammal.
31. Use of a system according to claim 22 for transvascularly
stimulating a nerve in a mammal.
32. Use of an electrode structure according to claim 1 for
transvascularly stimulating the phrenic nerve in a mammal.
33. Use of an electrode structure according to claim 1 for
transvascularly stimulating the trigeminal nerve in a mammal.
34. Use of an electrode structure according to claim 1 for
transvascularly stimulating the obturator nerve in the hip or groin
area of a mammal.
35. Use of an electrode structure according to claim 1 for
transvascularly stimulating the vagus nerve in the hip or groin
area of a mammal.
36. A nerve stimulation system comprising: a stimulation signal
generator; a first electrode structure comprising a first plurality
of electrodes and dimensioned to be implantable at a position along
a lumen of a person's left brachiocephalic vein that is proximate
to the left phrenic nerve; a second electrode structure comprising
a second plurality of electrodes dimensioned to be implantable at a
position along a lumen of the person's superior vena cava that is
proximate to the right phrenic nerve; and, means for transmitting
signals from the signal generator to the first and second
pluralities of electrodes.
37. A nerve stimulation system according to claim 36 wherein the
means for transmitting signals from the signal generator to the
first and second pluralities of electrodes comprises a plurality of
implantable electrical leads.
38. A nerve stimulation system according to claim 36 wherein the
means for transmitting signals from the signal generator to the
first and second pluralities of electrodes comprises a wireless
control signal transmission system.
39. A method for regulating breathing of a person, the method
comprising: implanting at least one of: a first electrode structure
at a position along a lumen of the left brachiocephalic vein that
is proximate to the left phrenic nerve; a second electrode
structure at a position along a lumen of the superior vena cava
that is proximate to the right phrenic nerve; a third electrode
structure at a position along a lumen of the left interior jugular
vein that is proximate to the left phrenic nerve; and a fourth
electrode structure at a position along a lumen of the right
interior jugular vein that is proximate to the right phrenic nerve;
stimulating at least one of the left- and right-phrenic nerves by
applying stimulation signals to electrodes of the first and second
electrode structures.
40. A method for regulating breathing of a person, the method
comprising: implanting a first electrode structure at a position
along a lumen of the left brachiocephalic vein that is proximate to
the left phrenic nerve; implanting a second electrode structure at
a position along a lumen of the superior vena cava that is
proximate to the right phrenic nerve; stimulating the left- and
right-phrenic nerves by applying stimulation signals to electrodes
of the first and second electrode structures.
41. A method according to claim 40 comprising inserting the first
and second electrode structures through a cannulation site in the
person's left brachiocephalic vein.
42. A method according to claim 41 comprising inserting the first
electrode structure and subsequently introducing the second
electrode structure through a bore of the first electrode
structure.
43. A method according to claim 40, wherein the electrode
structures each comprise an electrode supported on an
electrically-insulating backing sheet; and, a structure for holding
the backing sheet against the inner wall of a blood vessel with the
electrode in contact with the inner wall of the blood vessel and
the method comprises providing a balloon within the electrode
structure and inflating the balloon to urge the backing sheet
against an inner wall of the lumen of the blood vessel.
44. A system for providing assisted breathing to a person, the
system comprising at least one of: a first electrode structure
implanted at a position along a lumen of the person's left
brachiocephalic vein that is proximate to the left phrenic nerve; a
second electrode structure implanted at a position along a lumen of
the person's superior vena cava that is proximate to the right
phrenic nerve; and, a signal generator connected to apply
stimulation signals to electrodes of the first and second electrode
structures.
45. (canceled)
46. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. patent
application No. 60/887,031 filed on 29 Jan. 2007 and entitled
MINIMALLY INVASIVE NERVE STIMULATION METHOD AND APPARATUS. For the
Purposes of the United States of America, this application claims
the benefit under 35 U.S.C. .sctn.119 of U.S. patent application
No. 60/887,031 filed on 29 Jan. 2007 and entitled MINIMALLY
INVASIVE NERVE STIMULATION METHOD AND APPARATUS which is hereby
incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to neurophysiology and in particular
to apparatus and methods for stimulating nerves through the walls
of blood vessels. Aspects of the invention provide electrode
structures that may be deployed within blood vessels to stimulate
nerves passing near the blood vessels; nerve stimulation systems;
and methods for nerve stimulation. Aspects of the invention may be
applied for restoring breathing, treating conditions such as
chronic pain, and other uses involving nerve stimulation. Aspects
of the invention may be applied in the treatment of acute or
chronic conditions.
BACKGROUND
[0003] Nerve stimulation can be applied in the treatment of a range
of conditions. The nerve stimulation may be applied to control
muscle activity or to generate sensory signals. Nerves may be
stimulated by surgically implanting electrodes in, around or near
the nerves and driving the electrodes from an implanted or external
source of electricity.
[0004] The phrenic nerve normally causes the contractions of the
diaphragm that are necessary for breathing. Various conditions can
prevent appropriate signals from being delivered to the phrenic
nerve. These include: [0005] chronic or acute injury to the spinal
cord or brain stem; [0006] Amyotrophic Lateral Sclerosis (ALS);
[0007] disease affecting the spinal cord or brain stem; and, [0008]
decreased day or night ventilatory drive (e.g. central sleep apnea,
Ondine's curse). These conditions affect significant numbers of
people.
[0009] Mechanical ventilation may be used to help patients breathe.
Some patients require chronic mechanical ventilation. Mechanical
ventilation can be lifesaving but has a range of significant
problems. Mechanical ventilation: [0010] tends to provide
insufficient venting of the lungs. This can lead to accumulation of
fluid in the lungs and susceptibility to infection. [0011] requires
apparatus that is not readily portable. A patient on ventilation is
tied to a ventilator. This can lead to atrophy of muscles
(including breathing muscles) and an overall decline in well being.
[0012] can adversely affect venous return because the lungs are
pressurized. [0013] interferes with eating and speaking. [0014]
requires costly maintenance and disposables.
[0015] Phrenic nerve pacing uses electrodes implanted in the chest
to directly stimulate the phrenic nerve. The Mark IV Breathing
Pacemaker System available from Avery Biomedical Devices, Inc. of
Commack, New York USA is a diaphragmatic or phrenic nerve
stimulator that consists of surgically implanted receivers and
electrodes mated to an external transmitter by antennas worn over
the implanted receivers. Implanting electrodes and other
implantable components for phrenic nerve pacing requires
significant surgery. The surgery is complicated by the fact that
the phrenic nerve is small (approx. diameter 2 mm) and delicate.
The surgery involves significant cost.
[0016] Laproscopic diaphragm pacing being developed by Case Western
Reserve University bio-medical engineers and physician researchers
is another technique for controlling breathing. Devices for use in
Laproscopic diaphragm pacing are being developed by Synapse
Biomedical, Inc. Laproscopic diaphragm pacing involves placing
electrodes at motor points of the diaphragm. A laparoscope and a
specially designed mapping procedure are used to locate the motor
points.
[0017] References that in the field of nerve stimulation include:
[0018] Moffitt et al., WO 06/110338A1, entitled: TRANSVASCULAR
NEURAL STIMULATION DEVICE; [0019] Caparso et al., US 2006/0259107,
entitled: SYSTEM FOR SELECTIVE ACTIVATION OF A NERVE TRUNK USING A
TRANSVASCULAR RESHAPING LEAD; [0020] Dahl et al., WO 94/07564
entitled: STENT-TYPE DEFIBRILLATION ELECTRODE STRUCTURES; [0021]
Scherlag et al., WO 99/65561 entitled: METHOD AND APPARATUS FOR
TRANSVASCULAR TREATMENT OF TACHYCARDIA AND FIBRILLATION; [0022]
Bulkes et al., US20070288076A1 entitled: BIOLOGICAL TISSUE
STIMULATOR WITH FLEXIBLE ELECTRODE CARRIER; [0023] Weinberg et al.,
EP 1304135 A2 entitled: IMPLANTABLE LEAD AND METHOD FOR STIMULATING
THE VAGUS NERVE; [0024] Moffitt et al., US20060259107 entitled:
SYSTEM FOR SELECTIVE ACTIVATION OF A NERVE TRUNK USING A
TRANSVASCULAR RESHAPING LEAD; [0025] Denker et al. U.S. Pat. No.
6,907,285 entitled: IMPLANTABLE DEFIBRILLATOR WITH WIRELESS
VASCULAR STENT ELECTRODES; [0026] Chavan et al. US20070093875
entitled IMPLANTABLE AND RECHARGEABLE NEURAL STIMULATOR; [0027]
Rezai, U.S. Pat. No. 6,885,888 entitled ELECTRICAL STIMULATION OF
THE SYMPATHETIC NERVE CHAIN; [0028] Mehra, U.S. Pat. No. 5,170,802
entitled IMPLANTABLE ELECTRODE FOR LOCATION WITHIN A BLOOD VESSEL;
[0029] Mahchek et al. U.S. Pat. No. 5,954,761 entitled: IMPLANTABLE
ENDOCARDIAL LEAD ASSEMBLY HAVING A STENT; [0030] Webster Jr. et al.
U.S. Pat. No. 6,292,695 entitled: METHOD AND APPARATUS FOR
TRANSVASCULAR TREATMENT OF TACHYCARDIA AND FIBRILLATION; [0031]
Stokes, U.S. Pat. No. 4,643,201; [0032] Ela Medical SA, EP
0993840A, U.S. Pat. No. 6,385,492 [0033] WO 9407564 describes
stent-type electrodes that can be inserted through a patient's
vasculature. [0034] WO 9964105A1 describes transvascular treatment
of tachycarida. [0035] WO 9965561A1 describes a method and
apparatus for transvascular treatment of tachycardia and
fibrillation. [0036] WO02058785A1 entitled VASCULAR SLEEVE FOR
INTRAVASCULAR NERVE STIMULATION AND LIQUID INFUSION describes a
sleeve that includes an electrode for stimulating nerves. [0037] WO
06115877A1 describes vagal nerve stimulation using vascular
implanted devices. [0038] WO 07053508A1 entitled INTRAVASCULAR
ELECTRONICS CARRIER AND ELECTRODE FOR A TRANSVASCULAR TISSUE
STIMULATION SYSTEM and US20070106357A1 describe an intravascular
mesh type electrode carrier in which the conductor of a lead is
interwoven into the carrier mesh. [0039] U.S. Pat. No. 5,224,491
describes implantable electrodes for use in blood vessels. [0040]
U.S. Pat. No. 5,954,761 describes an implantable lead carrying a
stent that can be inserted into the coronary sinus. [0041] U.S.
Pat. No. 6,006,134 describes transvenous stimulation of nerves
during open heart surgery. [0042] U.S. Pat. No. 6,136,021 describes
an expandable electrode for coronary venous leads (the electrode
can be placed or retained in the vasculature of the heart). [0043]
Spreigl et al. U.S. Pat. No. 6,161,029 entitled: APPARATUS AND
METHOD FOR FIXING ELECTRODES IN A BLOOD VESSEL describes fixing
electrodes in blood vessels. [0044] U.S. Pat. No. 6,438,427
describes electrodes for insertion into the coronary sinus. [0045]
U.S. Pat. No. 6,584,362 describes leads for pacing and/or sensing
the heart from within the coronary veins. [0046] U.S. Pat. No.
6,778,854 describes use of electrodes in the Jugular vein for
stimulation of the Vagus nerve. [0047] U.S. Pat. No. 6,934,583
discloses stimulation of the Vagus nerve with an electrode in a
blood vessel. [0048] U.S. Pat. No. 7,072,720 describes catheter and
tube electrode devices that incorporate expanding electrodes
intended to contact the interior walls of blood vessels or anatomic
structures in which the electrode devices are implanted as well as
methods involving stimulation of the vagus nerve. [0049] U.S. Pat.
No. 7,184,829 discloses transvascular stimulation of a vagal nerve.
[0050] U.S. Pat. No. 7,225,019 discloses intravascular nerve
stimulation electrodes that may be used in the Jugular vein. [0051]
U.S. Pat. No. 7,231,260 describes intravascular electrodes. [0052]
Schauerte et al., US 2002/0026228 entitled: ELECTRODE FOR
INTRAVASCULAR STIMULATION, CARDIOVERSION AND/OR DEFIBRILLATION;
[0053] Jonkman et al., U.S. Pat. No. 6,006,134 [0054] Bonner et
al., U.S. Pat. No. 6,201,994 [0055] Brownlee et al., U.S. Pat. No.
6,157,862 [0056] Scheiner et al., U.S. Pat. No. 6,584,362 [0057]
Psukas, WO 01/00273 [0058] FR 2801509, US 2002065544 [0059] Morgan,
U.S. Pat. No. 6,295,475 [0060] Bulkes et al., U.S. Pat. No.
6,445,953 [0061] Rasor et al. U.S. Pat. No. 3,835,864 entitled:
INTRA-CARDIAC STIMULATOR [0062] Denker et al. US20050187584 [0063]
Denker et al. US20060074449A1 entitled: INTRAVASCULAR STIMULATION
SYSTEM WITH WIRELESS POWER SUPPLY; [0064] Denker et al.
US20070106357A1 entitled: INTRAVASCULAR ELECTRONICS CARRIER
ELECTRODE FOR A TRANSVASCULAR TISSUE STIMULATION SYSTEM; [0065]
Boveja et al. US20050143787 [0066] Transvenous Parassympathetic
cardiac nerve stimulation; an approach for stable sinus rate
control, Journal of Cardiovascular Electrophysiology 10(11) pp.
1517-1524 November 1999 [0067] Transvenous Parassympathetic nerve
stimulation in the inferior vena cava and atrioventricular
conduction, Journal of Cardiovascular Electrophysiology 11(1) pp.
64-69, January 2000. [0068] Planas et al., Diaphragmatic pressures:
transvenous vs. direct phrenic nerve stimulation, J. Appl. Physiol.
59(1): 269-273, 1985. [0069] Yelena Nabutovsky, M. S. et al., Lead
Design and Initial Applications of a New Lead for Long-Term
Endovascular Vagal Stimulation, PACE vol. 30, Supplement 1, January
2007 p. S215
[0070] Other references of interest include: [0071] Amundson, U.S.
Pat. No. 5,779,732
[0072] There remains a need for surgically simpler, cost-effective
and practical apparatus and methods for nerve stimulation.
SUMMARY OF THE INVENTION
[0073] This invention has a range of aspects. One aspect of the
invention provides electrodes for transvascular stimulation of
nerves. In embodiments, electrode structures comprise at least one
electrode supported on an electrically-insulating backing sheet;
and, a structure for holding the backing sheet against the inner
wall of a blood vessel with the electrode in contact with the inner
wall of the blood vessel. In some embodiments, the backing sheet is
designed to unroll inside the lumen of a blood vessel to fit around
the periphery of the lumen of a blood vessel. In such embodiments,
the backing sheet can comprise the structure for holding the
backing sheet against the inner wall of the blood vessel. In other
embodiments an expandable stent or a tube is provided to hold the
backing sheet and electrodes against the blood vessel wall.
[0074] Another aspect of the invention comprises a nerve
stimulation system comprising a stimulation signal generator and
first and second electrode structures. The first electrode
structure comprises a first plurality of electrodes and is
dimensioned to be implantable at a position along a lumen of a
person's left brachiocephalic vein that is proximate to the left
phrenic nerve. The second electrode structure comprises a second
plurality of electrodes and is dimensioned to be implantable at a
position along a lumen of the person's superior vena cava that is
proximate to the right phrenic nerve. The system comprises means
such as electrical leads, a wireless system or the like for
transmitting signals from the signal generator to the first and
second pluralities of electrodes.
[0075] Another aspect of the invention provides a method for
regulating breathing of a person. The method comprises implanting
at least one of: a first electrode structure at a position along a
lumen of the left brachiocephalic vein that is proximate to the
left phrenic nerve; and a second electrode structure at a position
along a lumen of the superior vena cava that is proximate to the
right phrenic nerve; and subsequently stimulating the left- and
right-phrenic nerves by applying stimulation signals to electrodes
of the first and second electrode structures.
[0076] Further aspects of the invention and features of specific
example embodiments of the invention are described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] The accompanying drawings illustrate non-limiting example
embodiments of the invention.
[0078] FIG. 1 shows a number of nerves adjacent to a blood
vessel.
[0079] FIG. 2 is a schematic diagram of a transvascular nerve
stimulation apparatus according to an example embodiment.
[0080] FIG. 3 is a cross section through an electrode structure
having multiple electrodes or rows of electrodes spaced apart
around an inner wall of a blood vessel.
[0081] FIGS. 4A, 4B and 4C are partially schematic cross sectional
views illustrating stages in the implanting of an electrode
structure according to an example embodiment which includes an
expandable stent in a blood vessel.
[0082] FIGS. 5A, 5B and 5C are partially schematic cross sectional
views illustrating an electrode structure according to an
embodiment having an engagement structure for holding the electrode
structure expanded against an inner wall of a blood vessel.
[0083] FIGS. 6 and 6A are respectively perspective and cross
sectional views showing an electrode structure according to another
embodiment wherein electrodes are held against an inner wall of a
blood vessel by a retention tube.
[0084] FIGS. 7A and 7B are perspective views showing an electrode
structure having four electrodes respectively in a flat
configuration and a rolled configuration. In the rolled
configuration, the electrodes face radially outward.
[0085] FIGS. 7C and 7F are views showing plan views of unrolled
electrode structures having electrodes that may be used in bipolar
pairs (among other electrical configurations). FIGS. 7D and 7E show
example ways for pairing the electrodes of the electrode structure
of FIG. 7C.
[0086] FIG. 7G is a perspective view showing an electrode structure
having four rows of electrodes in a rolled configuration in which
the electrode structure is curled up within an apertured insertion
tube.
[0087] FIG. 7H is a cross section through a blood vessel within
which an electrode structure according to another embodiment has
been placed.
[0088] FIGS. 8A and 8B are schematic illustrations of the use of a
structure comprising bi-polar electrodes to stimulate a nerve
extending transversely to a blood vessel.
[0089] FIG. 8C is a schematic illustrations of the use of a
structure comprising bi-polar electrodes to stimulate a nerve
extending generally parallel to a blood vessel.
[0090] FIG. 9 is a cut away view of a person's neck.
[0091] FIG. 9A is a cut away view illustrating a minimally invasive
transvascular nerve stimulation system installed in a person
according to an embodiment wherein an electrode structure is
disposed in the person's internal jugular vein in the neck or upper
chest region.
[0092] FIGS. 10A and 10B illustrate the anatomy of selected nerves
and blood vessels in a person's neck and upper torso.
[0093] FIG. 11 is a cut away view illustrating a minimally invasive
transvascular nerve stimulation system installed in a person
according to an embodiment wherein electrode structures are
disposed in one or both of the person's superior vena cava and left
brachiocephalic vein.
[0094] FIG. 12 is a cut away view illustrating a minimally invasive
transvascular nerve stimulation system installed in a person
according to an embodiment wherein control signals are transmitted
wirelessly to cause stimulation signals to be delivered at
electrode structures.
DESCRIPTION
[0095] Throughout the following description, specific details are
set forth in order to provide a more thorough understanding of the
invention. However, the invention may be practiced without these
particulars. In other instances, well known elements have not been
shown or described in detail to avoid unnecessarily obscuring the
invention. Accordingly, the specification and drawings are to be
regarded in an illustrative, rather than a restrictive, sense.
[0096] This invention relates to transvascular stimulation of
nerves. In transvascular stimulation, suitable arrangements of one
or more electrodes are positioned in a blood vessel that passes
close to a nerve to be stimulated. Electrical currents pass from
the electrodes through a wall of the blood vessel to stimulate the
nerve.
[0097] FIG. 1 shows three nerves, N1, N2 and N3 that pass nearby a
blood vessel V having a wall W defining a lumen L. FIG. 1 is
illustrative and not intended to represent any specific blood
vessel or nerves. FIG. 1 represents any suitable one of the various
places in the body where nerves pass nearby to veins or arteries.
Nerves N1 and N2 extend roughly parallel to blood vessel V and
nerve N3 extends generally transversely to blood vessel V, at least
in their parts depicted in FIG. 1. Nerve N1 is closer to blood
vessel V than nerve N2.
[0098] FIG. 2 illustrates schematically the use of an electrode
structure 10 inserted into lumen L of blood vessel V to stimulate
nerve N1. Electrode structure 10 comprises an electrode 12, an
electrically-insulating backing layer 14 and a means 15 for holding
electrode 12 and backing layer 14 in place against the inner wall
of blood vessel V. Electrode 12 may be attached to backing layer
14. This is not mandatory, however. It is sufficient that electrode
12 can be held against or at least in close proximity to the wall W
of the blood vessel and that backing layer 14 covers the side of
electrode 12 facing into lumen L. Various example structures that
may be used as means 15 are described below. Electrode structures
which provide electrodes backed by electrically-insulating barriers
as illustrated generally in FIG. 2 may be provided in a variety of
ways.
[0099] Electrode 12 is connected to a signal generator 18 by a
suitable lead 17. Signal generator 18 supplies electrical current
to electrode 12 by way of lead 17. Signal generator 18 may be
implanted or external to the body. Signal generator 18 may, for
example, comprise an implantable pulse generator (IPG).
[0100] In some embodiments electrode structure 10 includes a
circuit (not shown) for applying signals to one or more electrodes
12 and a battery, system for receiving power wirelessly or another
supply of electrical power. In such embodiments, signal generator
18 may deliver control signals which cause the circuit to apply
stimulation signals to electrode 12 by way of a suitable wireless
link technology. The wireless link may provide communication of the
control signals between a small transmitter associated with signal
generator 18 and a small receiver associated with electrode
structure 10. With suitably miniature circuitry, it may be possible
to provide a signal generator 18 that is co-located in a
sufficiently large blood vessel with electrode structure 10. The
signal generator 18 may, for example, comprise a thin electronic
circuit embedded within backing sheet 14.
[0101] Electrode 12 serves as a source or as a sink for electrical
current. Depending upon the nature of the electrical signals
generated by signal generator 18 electrode 12 may serve as a
current source at some times and as a current sink at other times.
Another electrode or group of electrodes (not shown in FIG. 2) in
contact with the patient serves to complete an electrical circuit.
The other electrode or group of electrodes may be incorporated in
electrode structure 10 (as is usually preferable) or may be
separate.
[0102] Electrically-insulating backing layer 14 presents a
high-impedance to the flow of electrical current and therefore
reduces the amount of current flow through the blood in blood
vessel V. It is not mandatory that layer 14 have an extremely high
electrical resistance. It is sufficient if layer 14 has a
resistance to the flow of electricity through layer 14 that is
significantly greater than that presented by the blood in blood
vessel V. Blood typically has a resistivity of about 120 to 190
.OMEGA.cm. In example embodiments, the blood in a blood vessel may
provide an electrical resistance between closely-spaced electrical
contacts that is inversely proportional to the dimensions of the
lumen of the blood vessel. In large blood vessels the longitudinal
electrical resistance between reasonable closely-spaced contacts
can be a few tens of ohms for example. Layer 14 preferably provides
an electrical resistance of at least a few hundred ohms, preferably
a few kilo ohms or more to the flow of electrical current through
the thickness of layer 14. Layer 14 could have electrically
conductive members such as leads and the like embedded within it or
electrically-conductive on its inner surface and still be
considered to be `electrically-insulating`.
[0103] By making layer 14 of a suitable material such as silicone
rubber elastomer, a biocompatible plastic, or another biocompatible
insulating material it is easily possible to provide a backing
layer 14 having a suitable resistance to the flow of electrical
current. FIG. 2 illustrates how the presence of backing layer 14
directs the electric field E (illustrated schematically in FIG. 2
by lines of equipotential) outwardly from blood vessel V.
[0104] In FIG. 2, the delivery of electrical stimulation to nerve
N1 is enhanced by: [0105] Locating electrode 12 against the
internal wall of blood vessel V at a location close to nerve N1;
[0106] Providing an electrode 12 having a relatively large contact
surface that can achieve a large contact area with the inner wall
of blood vessel V; [0107] Curving the contact surface of electrode
12 to roughly match the curvature of the inner face of blood vessel
V; [0108] Providing electrically-insulating backing sheet 14. With
these features, a significantly lower stimulation intensity is
required to stimulate target nerve N1 than would be the case for
wire electrodes located in lumen L in contact with the blood in
lumen L. Additionally, selectivity for a nerve of interest is
improved. Advantageously, electrodes 12 have active surface areas
in the range of about 1/2 mm.sup.2 to about 5 mm.sup.2. In some
embodiments, each electrode has an active surface area on the order
of 2 mm.sup.2.
[0109] Electrode structure 10 may be introduced into blood vessel V
in a minimally-invasive, safe way. Blood vessel V may be a
relatively large blood vessel that courses in the vicinity of the
target nerve N1. In some embodiments, electrode structure 10
comprises a flexible multi-contact electrode carrier sheet (ECS) of
suitable dimensions. The sheet may be tightly coiled prior to its
insertion into blood vessel V. Once within blood vessel V the sheet
may be allowed to unwind so as to bring electrode 12 into contact
with wall W of blood vessel V.
[0110] An electrode structure may support multiple electrodes. FIG.
3 shows an example electrode structure 20 which supports a number
of electrodes including electrodes 22A, 22B, 22C and 22D
(collectively electrodes 22). Other electrodes out of the plane of
FIG. 3 may also be present. In the illustrated embodiment,
electrodes 22A, 22B, 22C and 22D are circumferentially spaced
approximately equally around the perimeter of the inside wall of
blood vessel V. Each electrode 22 is insulated from the lumen of
blood vessel V by a thin flexible insulating sheet 24 (individually
identified as 24A, 24B, 24C and 24D. Each of the insulating sheets
24 is conformally disposed against the internal wall of blood
vessel V. In alternative embodiments, two or more electrodes are
disposed on a common insulating sheet. Insulating sheets 24 may be
joined together or may be different parts of a continuous
sheet.
[0111] E1, E2, E3 and E4 illustrate the areas corresponding to
electrodes 24A through 24D in which the electrical field associated
with current flow at the corresponding electrode is strong enough
to stimulate a nerve. Increasing the strength of the signal (e.g. a
stimulation pulse) at an electrode increases the affected area (as
indicated by the larger dotted regions).
[0112] FIG. 3 shows two nerves N4 and N5. It can be seen that a
stimulation signal from electrode 22A can stimulate nerve N4. A
stimulation signal from electrode 22B can stimulate nerve N5. The
arrangement of blood vessel V and nerves N4 and N5 is like the
arrangement of the internal jugular vein and the phrenic and vagus
nerves in the neck region of a person. With an arrangement as shown
in FIG. 3, a target phrenic nerve at the location of N4 can be
preferentially stimulated by electrode 22A due to greater proximity
of electrode 22A and also due to the shape of the area E1 affected
by electrode 22A. The vagus nerve at location N5 is usually
approximately diametrically opposite from electrode 22A and is not
affected by signals delivered at normal levels at electrode 22A.
The vagus nerve is, however, affected by signals delivered at
electrode 22C.
[0113] The phrenic nerve and vagus nerve in adult humans are each
typically about 2 mm in diameter. The lumen of the internal jugular
vein in adult humans is typically in the range of about 10 mm to 20
mm in diameter. The distance from the phrenic nerve to the internal
jugular vein and the distance from the vagus nerve to the internal
jugular vein are each typically in the range of about 2 mm to about
10 mm. Generally the phrenic nerve and vagus nerve are on opposite
sides of the internal jugular vein so that they are roughly 15 mm
to 30 mm apart from one another. This arrangement facilitates the
ability to perform transvascular stimulation of only the vagus
nerve or only the phrenic nerve without stimulating the other
nerve. A system according to some embodiments stimulates the
phrenic nerve or vagus nerve only. A system according to other
embodiments selectively stimulates either or both of the phrenic
and vagus nerves from an electrode structure located in the
internal jugular vein.
[0114] In many cases, nerves comprise a plurality of fascicles. For
example, in the example illustrated in FIG. 3, the phrenic nerve N4
is composed of three phrenic fascicles PF1, PF2, and PF3. These
phrenic fascicles may be selectively recruited by progressive
levels of stimulation current at electrode 22A. At lower
stimulation levels, only PF1 is recruited. At higher levels PF1 and
PF2 are both recruited. At still higher levels, all of PF1, PF2 and
PF3 are recruited. In FIG. 3, the vagus nerve N5 is composed of two
vagus fascicles VF1, and VF2 that may be selectively recruited by
progressive levels of stimulation current at electrode 22C. At
lower stimulation levels only VF1 is recruited. At higher
stimulation levels both VF1 and VF2 are recruited.
[0115] It is desirable that an electrode structure provide a
minimum obstruction to the flow of blood in lumen L of a blood
vessel V. Therefore, electrode structures are preferably thin in
comparison to the inner diameter of blood vessel V. In some
embodiments, a structure that supports electrodes and insulating
backing sheets gently urges the electrodes and insulating backing
sheets radially outward in lumen L so as to leave an open passage
for blood flow past the electrode structure. To prevent the
disruption or blockage of blood flow in a blood vessel, the
cross-sectional area of an intravascular electrode structure should
not exceed a certain fraction of the cross-sectional area of the
lumen of the blood vessel. A round blood vessel with an internal
diameter of 10 mm has a cross-sectional area of approximately 75
mm.sup.2. The circumference of the electrode structure when
expanded in the blood vessel should preferably not be greater than
about 10.times..pi. mm, (approximately 30 mm). If the thickness of
an electrode structure is between about 0.3 and 0.5 mm then the
cross-sectional area of the electrode structure will be about 10
mm.sup.2 to 15 mm.sup.2, which represents less than 20% of the
lumen of the vessel.
[0116] FIGS. 4A, 4B and 4C show an electrode structure 30 according
to an example embodiment. Electrode structure 30 comprises a
plurality of electrodes 32 disposed on a flexible
electrically-insulating sheet 34. Electrode structure is initially
introduced into a blood vessel V tightly curled up around an
expandable stent 35 inside an introducer tube 36. Stent 35 may, for
example, comprise an expandable wire stent. A variety of suitable
expandable wire stents is available from medical devices
manufacturers.
[0117] Electrode structure 30 is guided to a desired location in a
blood vessel V inside introducer tube 36. At the desired location,
introducer tube 36 is retracted to allow electrically-insulating
sheet 34 to begin to unroll as shown in FIG. 4B. Stent 35 is then
expanded in order to further unroll electrically-insulating sheet
34 and to urge electrically insulating sheet 34 and the electrodes
32 carried on electrically-insulating sheet 34 against the inner
wall of blood vessel V as shown in FIG. 4C.
[0118] In the illustrated embodiment, stent 35 is attached to sheet
34 at a point, row of points or line 37. Stent 35 is left in place
to retain electrodes 32 and sheet 34.
[0119] Stent 35 may comprise any suitable type of expandable stent.
A wide range of such stents are known. Stent 35 is expanded in a
manner appropriate to the stent. For example, in some embodiments a
balloon is placed inside the stent and the stent is expanded by
inflating the balloon. The balloon may be withdrawn after the stent
has been expanded.
[0120] FIGS. 5A, 5B and 5C illustrate an electrode structure 40
which is similar to electrode structure 30 except that it has
electrodes 42 supported on a flexible sheet 44 and an engagement
mechanism 47 which allows opposed edges portions 44A and 44B of
flexible sheet 44 to be locked together when flexible sheet 44 has
been opened within the lumen L of blood vessel V. The locking
together of edge portions 44A and 44B holds flexible sheet 44 in an
expanded configuration with electrodes 42 contacting the inner
surface of wall W. Electrode structure 40 does not have a stent
inside flexible sheet 44 (although a stent could optionally be
added to provide further support for sheet 44). Sheet 44 may be
made so that it has a tendency to unroll toward a configuration
that is less tightly-rolled than shown in either of FIG. 5A or 5B.
This tendency will bias sheet 44 to open into the configuration of
FIG. 5B when removed from insertion tube 46 and will help to hold
sheet 44 in place inside blood vessel V.
[0121] In the illustrated embodiment, mechanism 47 comprises mating
sets of ridges 47A and 47B that extend longitudinally respectively
along edge portions 44A and 44B. Ridges 47A and 47B are on opposing
major surfaces of sheet 44 so that they can contact one another
when sheet 44 is sufficiently unrolled. As shown in FIG. 5B, ridges
47A and 47B interlock when sheet 44 is unrolled as fully as the
dimension of blood vessel V will permit. Mechanism 47 thus serves
to retain sheet 44 and electrodes 42 snugly against the inside of
wall W and prevent sheet 44 from curling inwardly or moving away
from the wall W.
[0122] In preferred embodiments, mechanism 47 permits engagement of
edge portions 44A and 44B in a range of degrees of overlap. Thus,
mechanism 47 allows engagement of edge portions 44A and 44B when
sheet 44 has been expanded against the inner wall of blood vessels
having sizes within a given range of different sizes.
[0123] Alternative engagement mechanisms 47 are possible. For
example, in some embodiments, a biocompatible adhesive is
introduced between edge portions 44A and 44B. In other embodiments,
ridges or other interlocking features and a biocompatible glue are
both used.
[0124] An electrode structure 40 may be placed in a desired
location by: introducing and sliding the electrode structure along
a blood vessel to a desired location; at the desired location,
sliding electrode structure 40 out of tube 46; if electrode
structure 40 is partially or entirely self-unwinding, allowing
electrode structure 40 to unwind; and, if necessary, inflating a
balloon 49 to fully expand electrode structure 40 and/or engage
engagement mechanism 47. Introducing the electrode structure may
comprise cannulating the blood vessel and introducing the electrode
structure at the cannulation site.
[0125] FIG. 5C illustrates a method for removing or relocating an
electrode structure 40. Electrode structure 40 comprises a tab 48
or other projection that is attached to sheet 44 near or at an
inside edge thereof and is graspable from within lumen L. A tool 50
is inserted into lumen L and has jaws 51 operable to grasp tab 48.
At position 50A jaws 51 of tool 50 are opened to receive tab 48. At
position 50B, jaws 51 have been operated to grasp tab 48. At
position 50C tool 50 has been moved toward the center of lumen L
and tool 50 has thereby peeled the inner edge of sheet 44 away from
wall W. Tool 50 may be rotated about its axis to roll electrode
structure 40 into a smaller configuration. Electrode structure 40
may then be moved along blood vessel 44 to a new position; or
pulled into an insertion tube for safe removal from blood vessel
V.
[0126] FIGS. 6 and 6A show an electrode structure 70 that includes
a rolled, flexible electrically-insulating sheet 74 carrying
electrodes 72. Sheet 74 may be opened by partial unrolling within a
blood vessel V. A tubular retainer 73 may then be inserted to
retain sheet 74 and electrodes 72 in place against a wall of the
blood vessel. In cases where electrode structure 70 is to be
inserted into the blood vessel through an incision that is smaller
than the lumen of the blood vessel then tubular retainer 73 may be
expandable so that it can be introduced through the opening and
then expanded to a size suitable for retaining sheet 74 and
electrodes 72.
[0127] Retainer 73 has a diameter selected such that, when placed
inside sheet 74, it will retain sheet 74 and electrodes 72 in close
apposition to the inside wall of the blood vessel for as long as
required. The outside diameter of retainer 73 is chosen to closely
match the inner diameter of the blood vessel V minus twice the
thickness of sheet 74. For example, for a blood vessel with an
inside diameter of 10 mm and an electrode structure 70 with sheet
thickness of 1/2 mm, the outside diameter of retainer 73 should be
approximately 10 mm-21/2 mm=9 mm. Retainers 73 in a range of
diameters may be provided to allow a surgeon to select and insert
the best size. In typical blood vessels having inner diameters of
10 mm or more, the length of retainer 73 should be at least about
twice its diameter to ensure that retainer 73 will not tilt inside
the blood vessel. The wall thickness of retainer 73 may be fairly
small, for example, up to about 0.3 mm or so. Retainer 73 may be
made of a suitable material such as a biocompatible metal (e.g.
stainless steel or titanium) or a high-strength biocompatible
polymer.
[0128] Wires 75 carry signals from a signal generator to electrodes
72. In an alternative embodiment, a signal generator is integrated
with electrode structure 70. Such as signal generator may be
controlled to issue stimulation pulses in response to control
signals provided by way of a suitable wireless link.
[0129] FIGS. 7A to 7G show examples of electrode structures.
Electrode structure 80 of FIG. 7A has four electrodes 82
(individually 82A to 82D) supported on a major face 81 of a
flexible insulating sheet 84. Insulated leads 85 connect electrodes
82 to a signal generator (not shown in FIG. 7A). Sheet 84 may
comprise a flexible layer of silicone for example. Electrodes 82
and electrode leads 85 may be of any suitable shape and material;
e.g., stainless steel or platinum-iridium multi-stranded wire
electrodes with Teflon.TM. coated wire leads.
[0130] An electrode structure 80 may be fabricated, for example, by
connecting suitable electrodes to coated wire leads and then
embedding the electrodes and leads in a layer of silicone such that
the electrodes are exposed on one major face of the silicone layer
but not the other.
[0131] Electrode structure 80 may be used to stimulate nerves by
inserting electrode structure 80 into a blood vessel with
electrodes 82 facing outwardly; and connecting any one electrode to
the negative output of a standard constant-current (preferably) or
constant-voltage nerve stimulator (cathodic stimulation) with
respect to a remote reference electrode. Alternatively, any two
electrodes 82 can be selected as anode and cathode.
[0132] Electrode structure 80 is similar to a nerve cuff but
`inside out`. Each electrode preferentially stimulates a sector of
tissue that radiates outwardly from a blood vessel V and spans a
limited angle. For example, in an electrode structure having four
electrodes disposed approximately every 90 degrees around the
circumference of a blood vessel, the volume of tissue affected by
each electrode may span approximately 90 degrees (see FIG. 3 for
example).
[0133] A further improvement in angular selectivity may be obtained
by providing longitudinal ridges on the outer major surface of
electrode structure 80. The ridges enhance the electrical
separation between circumferentially-adjacent electrodes 82. The
ridges may be similar to the ridges described in Hoffer et al. U.S.
Pat. No. 5,824,027 entitled NERVE CUFF HAVING ONE OR MORE ISOLATED
CHAMBERS which is hereby incorporated herein by reference. Ridges
86 are shown schematically in FIG. 7A.
[0134] Optionally, sheet 84 may include geometrical complexities
such as holes or protuberances to provide a better substrate for
connective tissue adhesion and so increase the long-term mechanical
stability and immobility of structure 80 inside a blood vessel.
[0135] FIG. 7B shows an electrode structure like electrode
structure 80 wrapped into a tight spiral with electrodes facing out
in preparation for insertion into a blood vessel.
[0136] FIG. 7C shows an electrode structure 90 according to another
embodiment. Electrode structure 90 comprises a flexible sheet 94
that supports four pairs of electrodes 92. Sheet 94 may comprise a
thin flexible silicone sheet, for example. Electrical leads 93 are
provided to connect corresponding electrodes 92 to a signal source.
Electrodes and electrode leads may be of any suitable shape and
material; e.g., stainless steel or platinum-iridium multi-stranded
wire with Teflon.TM. coated leads. In the illustrated embodiment,
electrode contact surfaces are exposed through electrode windows in
which insulation of the leads is not present. Electrodes 92A and
92E; 92B and 92F; 92C and 92G; and 92D and 92H may be paired, for
example, as shown in FIG. 7D. As another example, electrodes 92A
and 92B; 92C and 92D; 92E and 92F; and 92G and 92H may be paired as
shown in FIG. 7E.
[0137] Electrode structure 90 may be applied to stimulate a nerve
or nerves by inserting electrode structure 90 into a blood vessel
with electrodes 92 facing outwardly; and connecting any two
electrodes 92 to the negative and positive outputs of a standard
constant-current or constant-voltage nerve stimulator. An effective
mode of stimulation is to select a pair of electrodes that are
aligned along a line that is generally parallel to the target
nerve, such that the greatest potential difference during
stimulation will be generated along the nerve axons in the target
nerve. Since the target nerve and target blood vessel may not be
strictly parallel to one another, it is useful to have multiple
electrodes in an electrode structure from which the pair of
electrodes that provide the greatest stimulation selectivity for a
target nerve can be identified by trial and error.
[0138] FIG. 7F shows an electrode structure 90A that is like
electrode structure 90 except that it includes ridges 91 of
electrically-insulating material that extend between groups of
electrodes 92.
[0139] FIG. 7G shows an electrode structure like electrode
structure 90 prepared for insertion into a blood vessel. Electrode
structure 90 is rolled up into a spiral and held by an outside
retainer 95. Outside retainer 95 has relatively thin walls. For
example, the wall thickness may be about 1/2 mm or less in some
embodiments. Apertures 96 penetrate the wall of outside retainer 95
and allow flow of electrical currents. Apertures 96 could
optionally be filled with electrically-conducting plugs.
[0140] At least one electrode 92 of electrode structure 90 is
electrically exposed to the surroundings through an aperture 96. As
the electrode structure is being advanced toward an intravascular
target location (the target location may be determined in advance
from an imaging survey study for each patient, and monitored with
fluoroscopy during the ECS implant procedure), electrodes 92 are
energized. Since at least some electrodes 92 are exposed by way of
apertures 96 the target nerve will be stimulated when electrode
structure 90 is close enough to the target nerve. An effect of
stimulation of the target nerve can be watched for in order to
determine when electrode structure has reached the vicinity of the
target nerve. The response may be monitored to fine tune the
position of electrode structure 90 in a blood vessel. Outside
retainer 95 may be removed when electrode structure 90 is at the
target location. Outside retainer 95 is tethered by a tether 97 so
that it can be recovered after deployment of structure 90.
[0141] FIG. 7H shows structure 90 at its intended location in blood
vessel V. Outer retainer 96 has been removed and the structure 90
has been allowed to unwind and deploy against the inside wall of
blood vessel V. The width (circumferential dimension) of structure
90 is chosen to closely match the inside perimeter of blood vessel
V at the target location. The inside dimension of the blood vessel
V may have been previously determined from ultrasound imaging,
balloon catheter, magnetic resonance imaging or other non-invasive
or minimally-invasive imaging technique.
[0142] When electrode structure 90 is at its desired position for
optimal stimulation of the target nerve, the outer retainer 95 is
gently removed and withdrawn from the patient's body while
structure 90 is kept in place, if needed, by means of a semi-rigid
rod-like tool (not shown) that is temporarily used to stabilize
structure 90 and prevent it from moving while outer retainer 95 is
withdrawn. As the outer retainer 95 is withdrawn, structure 90 will
naturally and rapidly unwrap toward its preferred
enlarged-cylindrical (or near-planar in some embodiments)
configuration and will stretch out against the inside wall of the
blood vessel with electrodes 92 disposed outwardly in close contact
to the blood vessel wall.
[0143] As noted above, the choice of electrodes to use to stimulate
a target nerve can depend on the orientation of the target nerve
relative to the blood vessel in which an electrode structure is
deployed. Where a target nerve passes more or less at right angles
to a blood vessel, it can be most efficient to stimulate the target
nerve by passing electric current between two electrodes that are
spaced apart circumferentially around the wall of the blood vessel.
In such cases it may be desirable to provide elongated electrodes
that extend generally parallel to the blood vessel (e.g. generally
parallel to an axis of curvature of the electrode structure). Such
elongated electrodes may be emulated by a row of smaller electrodes
that are electrically connected together.
[0144] FIGS. 8A and 8B show a nerve N extending transversely to a
blood vessel V. In the illustrated embodiment, the nerve extends
generally at right angles to the blood vessel. An electrode
structure 54 comprising first and second electrodes 55A and 55B
(collectively electrodes 55) is located in lumen L of blood vessel
V. Electrodes 55 are each close to or pressed against the inner
face of wall W of blood vessel V. Electrode structure 54 may have
additional electrodes as well as other features such as a structure
for holding electrodes 54 in place however these are not shown in
FIG. 8A or 8B for clarity. Electrodes 55A and 55B are spaced apart
from one another in a circumferential direction around the
periphery of blood vessel V. Electrodes 55 are ideally disposed in
a plane in which nerve N lies and which intersects blood vessel V
perpendicularly. Precise placement of the electrodes in such a
configuration is not mandatory. Electrodes 55 are spaced apart in a
direction that is generally along an axis of nerve N.
[0145] Each electrode 55 is protected against electrical contact
with the blood in lumen L of blood vessel V by an insulating
backing member 56. In the illustrated embodiment, backing members
56 comprise hollow insulating caps that may, for example, have the
form of hollow hemispheres. An edge of each insulating cap contacts
wall W of blood vessel V around the periphery of the corresponding
electrode 55.
[0146] In this embodiment, electrodes 55 are connected in a
bi-polar arrangement such that one electrode acts as a current
source and the other acts as a current sink. It is not mandatory
that the polarities of electrodes 55 always stay the same. For
example, in some stimulation modes the polarities could be
switched. In the illustrated embodiment, electrode 55A is connected
as a cathode (negative) electrode while electrode 55B is connected
as an anode (positive) electrode to a signal source (not shown in
FIG. 8A or 8B). When a stimulation signal is applied between
electrodes 55 an electric field is created. The electric field
causes small electrical currents to flow between electrodes 55 by
way of the surrounding tissues.
[0147] Since electrodes 55 are insulated from the lumen of blood
vessel V, electric current flows out of the current source
electrode 55A through wall W and surrounding tissues and returns to
the current sink electrode 55B. The stimulation current flows
longitudinally through the nerve N in the direction shown by arrows
F. For stimulation pulses of sufficient duration and intensity, the
nerve axons in target nerve N will generate action potentials that
will be conducted along the stimulated axons in nerve N.
[0148] Where a target nerve extends generally parallel to a blood
vessel it can be efficient to stimulate the target nerve by passing
electric current between two electrodes that are spaced apart
longitudinally along the wall of the blood vessel.
[0149] FIG. 8C shows a nerve N extending parallel to a blood vessel
V. An electrode structure 88 having first and second electrodes 89A
and 89B (collectively electrodes 89) is located inside blood vessel
V with electrodes 89A and 89B close to, preferably against the
inside of the wall W of blood vessel V. Electrode structure 88 may
have additional electrodes as well as other features such as a
structure for holding electrodes 89 in place however these are not
shown in FIG. 8C for clarity. Electrodes 89A and 89B are spaced
apart from one another in a longitudinal direction along blood
vessel V. The electrodes are ideally disposed on a line extending
parallel to an axis of the blood vessel although precise placement
of the electrodes in such a configuration is not mandatory.
[0150] In this embodiment, electrodes 89A and 89B are connected in
a bi-polar arrangement such that one electrode acts as a current
source and the other acts as a current sink. It is not mandatory
that the polarities of electrodes 89A and 89B always stay the same.
For example, in some stimulation modes the polarities could be
switched.
[0151] In the illustrated embodiment, electrode 89A is connected as
a cathode (negative) electrode while electrode 89B is connected as
an anode (positive) electrode to a signal source (not shown in FIG.
8C). Each electrode 89 is protected against electrical contact with
the blood in lumen L of blood vessel V by an insulating backing
member 87. In the illustrated embodiment, the backing members
comprise hollow insulating caps that may, for example, have the
form of hollow hemispheres. An edge of each insulating cap contacts
the wall of blood vessel V around the periphery of the
corresponding electrode 89.
[0152] Since electrodes 89 are electrically insulated from the
blood in lumen L of blood vessel V, electric current flows out of
the current source (e.g. cathode 89A), through wall W and
eventually returns to the current sink (e.g. anode electrode 89B).
This results in a stimulation current that flows longitudinally
through nerve N in the direction shown by arrows F. For stimulation
pulses of sufficient duration and intensity, the nerve axons in the
target nerve will generate action potentials that will be conducted
along the stimulated axons in nerve N.
[0153] Stimulating the phrenic nerves to regulate or cause
breathing is an example application of electrode structures as
described herein. The present invention provides a surgically
simple, lower risk response to the need of stimulating the phrenic
nerves to control the movement of the diaphragm and restore normal
breathing rate in people who have lost control of diaphragm due to
a central neurological lesion such as a high cervical spinal cord
injury or disease, including quadriplegia; central alveolar
hypoventilation; decreased day or night ventilatory drive (e.g.
central sleep apnea, Ondine's Curse) or brain stem injury or
disease. Phrenic nerves may be stimulated on an acute care or
chronic basis.
[0154] The phrenic nerves provide the major nerve supply to the
diaphragm. Each phrenic nerve contributes predominantly motor
fibres solely to its hemidiaphragm. The passage taken by the right
and left phrenic nerves through the thorax is different. This is
largely due to the disposition of great vessels within the
mediastinum. Occasionally, the phrenic nerve may be joined by an
accessory phrenic nerve.
[0155] The phrenic nerve on both sides originates from the ventral
rami of the third to fifth cervical nerves. The phrenic nerve
passes inferiorly down the neck to the lateral border of scalenus
anterior. Then, it passes medially across the border of scalenus
anterior parallel to the internal jugular vein which lies
inferomedially. At this point the phrenic nerve is deep to the
prevertebral fascia, the transverse cervical artery and the
suprascapular artery.
[0156] At the anterior, inferomedial margin of scalenus anterior
and hence superficial to the second part of the right subclavian
artery, the right phrenic nerve passes medially to cross the
pleural cupola deep to the subclavian vein. More medially, it
crosses the internal thoracic artery at approximately the level of
the first costochondral junction.
[0157] Within the thorax the right phrenic nerve is in contact with
mediastinal pleura laterally and medially, in succession from
superior to inferior, the following venous structures: right
brachiocephalic vein, superior vena cava, pericardium of the right
atrium, inferior vena cava. From the level of the superior vena
cava it is joined by the pericardiophrenic artery and both run
inferiorly anterior to the lung root. The right phrenic nerve
pierces the diaphragm in its tendinous portion just slightly
lateral to the inferior vena caval foramen. It then forms three
branches on the inferior surface of the diaphragm: anterior,
lateral and posterior. These ramify out in a radial manner from the
point of perforation to supply all but the periphery of the
muscle.
[0158] At the anteroinferior medial margin of scalenus anterior,
the left phrenic nerve crosses the first part of the left
subclavian artery and then the internal thoracic artery sited
slightly inferiorly. Passing inferiorly with the internal thoracic
artery laterally, it lies deep to the left brachiocephalic vein and
the left first costochondral joint. It receives a pericardiophrenic
branch of the internal thoracic artery which stays with its distal
course.
[0159] Within the thorax, the left phrenic nerve continues
inferiorly and slightly laterally on the anterolateral aspect of
the arch of the aorta, separated from the posterior right vagus
nerve by the left superior intercostal vein. Then it descends
anterior to the root of the left lung intermediate to fibrous
pericardium medially and parietal pleura laterally. Finally, it
curves inferiorly and anteriorly to reach the surface of the
diaphragm which it pierces anterior to the central tendon and
lateral to the pericardium. It then forms three branches on the
inferior surface of the diaphragm: anterior, lateral and posterior.
These ramify out in a radial manner from the point of perforation
to supply all but the periphery of the muscle.
[0160] The accessory phrenic nerve on each side occurs in roughly
15-25% of people. It originates as a branch of the fifth cervical
nerve which would otherwise pass to the subclavius. The accessory
phrenic nerve begins lateral to the phrenic nerve in the neck and
obliquely traverses the anterior surface of scalenus anterior as it
descends. It joins the phrenic nerve at the root of the neck to
descend to the diaphragm.
[0161] FIG. 9 shows the anatomy of the neck and, in particular, the
relative locations of phrenic nerve (PhN), vagus nerve (VN) and
internal jugular vein (IJV). Note that the IJV courses between the
PhN and VN. The PhN merges with the IJV and the three structures
run together distally at level of the clavicle (indicated by circle
99).
[0162] In one example embodiment illustrated in FIG. 9A, a
minimally invasive nerve stimulation system (`MINS`) 100 comprising
a flexible intravascular electrode array 101, for example, an
electrode structure of one of the embodiments described above is
permanently placed inside a target blood vessel V (in this example
the left Internal Jugular Vein, IJV) in close proximity to a target
nerve (in this example the left phrenic nerve PhN). One or more
electrodes of the electrode array is disposed for selective
stimulation of the PhN. Other electrodes are optionally disposed
for selective stimulation of a second target nerve, in this example
the left vagus nerve VN.
[0163] The electrode leads 104 from electrode array 101 emerge from
the cannulated BV at the original venous penetration site, C, and
then course subcutaneously to connectors 105 that connect to the
header of an implanted pulse generator 102 that is surgically
placed in a standard subcutaneous pocket. The pocket may be in the
upper chest wall for example. FIG. 9 shows only one electrode array
101 on the left side of the neck.
[0164] In this embodiment, the implanted MINS 100 stimulates the
left PhN to assist breathing by causing rhythmic inspiratory
movements of the diaphragm muscle (not shown in FIG. 9). Another
electrode array may additionally be implanted in a blood vessel on
the right side of the patient's body. For example, another
electrode array 101 may be implanted in the right internal jugular
vein for selective stimulation of the right PhN and, optionally,
also the right VN, if so desired. The additional electrode array
may be connected to internal pulse generator 102 or to a second
internal pulse generator (not shown in FIG. 9).
[0165] MINS 100 may be installed percutaneously using standard
procedures for the installation of deep catheters, cannulas, leads
or other intravascular device. Such procedures are described in the
medical literature. Once an electrode array has been introduced to
a location near the target location in the internal jugular vein
then the position of the electrode array may be fine-tuned by
applying low-current stimulation signals to one or more of the
electrodes in electrode array 101 and observing the patient's
breathing.
[0166] FIGS. 10A and 10B illustrate the anatomy of the neck and
chest and, in particular, the relative locations of the left and
right phrenic nerves (PhN), vagus nerves (VN), internal jugular
veins (IJV), brachiocephalic veins (BCV) and superior vena cava
(SVC). The PhNs run approximately perpendicular to and close to the
BCVs in areas 107R and 107L near the IJV/BCV junctions.
[0167] Each PhN may have more that one branch. The branches may
join together at variable locations ranging from the neck region to
the chest region below the IJV/BCV junctions. In the latter case,
branches of the PhN on either side of the body may course on
opposite sides of the BCVs. Two branches of the right PhN are
labeled PhN-1 and PhN-2 in FIG. 10B. The right PhN may include
branches that course on either side of the SVC. The left and right
PhN extend respectively to left and right hemi-diaphragms (HD).
[0168] FIG. 11 shows a MINS 110 having electrode structures 111L
and 111R (collectively 111) located respectively in a patient's
left BCV and SVC vessels near the left- and right-PhN respectively.
Leads 112L and 112R (collectively 112) respectively connect the
electrodes of left- and right-electrode structures 111L and 111R to
a signal generator. In the illustrated embodiment, the signal
generator comprises an implantable pulse generator (IPG) 115.
Alternatively, as described above, some or all functions of pulse
generator 115 may be provided by circuitry that is co-located with
or integrated with one or both of electrode structures 111. In some
embodiments, pulse generator 115 generates control signals that are
transmitted by way of a wireless communication link to cause
circuitry that is local to electrode structures 111 to apply
stimulation pulses by way of electrodes on electrode structures
111.
[0169] The implantable pulse generator may be configured to deliver
electrical pulses to electrodes of the left- and right electrode
structures 111 more-or-less simultaneously so that the left- and
right- hemidiaphragms are induced to undergo breathing motions in a
synchronized manner. IPG 115 may, for example, apply bursts of
stimulus pulses at a rate of about 12 or 13 bursts per minute. Each
burst may, for example, comprise 20-40 current pulses delivered at
a rate of 20 Hz or so and last roughly 1 to 2 seconds. Each burst
induces signals in the phrenic nerve that cause the diaphragm to
move to provide inspiration. Expiration occurs between bursts.
[0170] MINS 110 can be readily installed as shown in FIG. 11.
Electrode structures 111R and 111L may both be introduced through
the same intravascular insertion point C1 in the left BCV. In some
embodiments, electrode structure 111L is installed first. In such
embodiments, electrode structure 111L can be passed through the
left BVC past electrode structure 111L (e.g. through a bore of
electrode structure 111L) to its target location in the SVC.
Flexible leadout cables 112R passes through electrode structure
111L. Both leadout cables 112 emerge from the BCV and course
subcutaneously to a subcutaneous pocket area in the upper chest
where the leadout cable connectors are connected to IPG 115.
[0171] Locating initial target positions for electrode structures
111 is facilitated because the SVC, heart and BCV can be readily
visualized using available imaging techniques. It is known that the
phrenic nerves pass tightly past the heart on each side. Therefore,
target locations in the blood vessels within .+-.1 to 2 cm of the
optimum positions for stimulating the phrenic nerves can be
determined readily from images of the upper chest and lower
neck.
[0172] The arrangement shown in FIG. 11 has the advantage that the
distance from electrode structures 111 to the target nerves in
these locations may be smaller, more uniform and more reproducible
than for similar electrodes implanted in more proximal locations in
the IJVs where the target PhNs run parallel to the IJVs, but at
more variable distances (see FIG. 9, for example).
[0173] MINS 110 may be varied by leaving out one of electrode
structures 111 and its associated cable 112. Such embodiments may
be useful in acute care environments where it is necessary to
provide breathing assistance using a simple quick procedure. Such
embodiments may also be useful in chronic situations where
stimulation of one hemi-diaphragm is sufficient. Where only one
electrode structure 111 is implanted, the electrode structure may
be at either the location of electrode structure 111R or the
location of electrode structure 111L.
[0174] FIG. 12 shows a minimally-invasive nerve stimulation system
120 that is like MINS 110 of FIG. 11 but provides a wireless
connection between an implantable pulse generator and circuits
which deliver stimulation signals to electrodes. System 120 has two
sets of intravascular electrodes 121A and 121B. In some
embodiments, each set of electrodes comprises an electrode
structure as described herein. Each set of electrodes 121A and 121B
is connected by short flexible lead wires 123 to an associated RF
receiver unit 124. RF receiver units receive wireless stimulation
commands 125 from an implanted pulse generator 126 having an
associated transmitter (which is built into implantable pulse
generator 126 in the illustrated embodiment.
[0175] Each receiver unit 124 may comprise a hermetic package
containing an antenna and circuitry to decode command signals and
deliver stimulation pulses to the electrodes of the corresponding
electrode array 121. Each receiver unit may be attached to an
autonomous stent-like structure for safe, permanent and stable
installation in a blood vessel near the associated electrode array
121. The receiver units may be powered by the RF signal received
from implantable pulse generator 126. In such cases, the receiver
units do not require internal batteries.
[0176] Implantable pulse generator 126 may contain batteries or
another source of electrical energy, control circuitry and
transmitter antennas to communicate with receiver units 124 and
with an external programmer (not shown) that allows a therapist to
program the implanted system.
[0177] In some embodiments, an implantable pulse generator or other
signal source may have a primary battery or a rechargeable battery
that can be periodically recharged through the patient's skin. In
either case, it is desirable that the battery or other source of
electrical power have an expected life span such that it will not
require replacement for a reasonable period such as at least about
3 to 5 years.
[0178] Methods of stimulating the phrenic nerves, as described
herein can have the advantages that: [0179] electrodes do not come
into contact with the delicate phrenic nerves; [0180] there is no
implanted structure that interferes with movement of the diaphragm;
[0181] the system may be implanted and self-contained such that no
wires cross the skin; [0182] access to both the right and left
phrenic nerves can be provided through a single point of entry;
[0183] a control system, such as an implantable pulse generator may
be placed in reasonably close proximity to an electrode structure
so as to facilitate wireless control over the delivery of
stimulation pulses at the electrode structure by the implantable
pulse generator.
[0184] The applications of the apparatus and methods described
herein are not limited to phrenic and vagus nerves. The apparatus
and methods described herein may be applied to provide surgically
simple, low risk solutions for stimulating a wide range of
peripheral or cranial nerves. For example, the methods and
apparatus may be applied to stimulate the obturator nerve in the
hip/groin area or the trigeminal nerve in the head.
[0185] The apparatus and methods may be applied to treatment of a
wide variety of disorders such as pain of peripheral or
craniofacial origin, sensory deficits, paralysis or paresis of
central origin, autonomic disorders, and generally any medical
condition that can be treated or alleviated using neuromodulation
by electrical stimulation of a nerve that is in close proximity to
a larger blood vessel into which a flexible multi-channel electrode
array can be deployed.
[0186] Advantageously, implantation of electrode structures in
blood vessels is reversible and does not require surgical
intervention directly involving the target nerves.
[0187] In some embodiments, signal generator 115 has sensors that
sense a condition of the patient and adjust stimulation of the
phrenic nerve based on input from the sensors. The sensors may
detect things such as one or more of: [0188] whether the patient is
speaking or preparing to speak; [0189] whether the patient is lying
down or sitting or standing; [0190] whether the patient is awake or
asleep; [0191] blood oxygen concentration; [0192] blood CO.sub.2
concentration; [0193] etc. In response to the sensor signals, the
signal generator may adapt the pattern or rate of breathing. For
example: [0194] Breathing could be automatically suppressed when a
sensor signal indicates that the patient is attempting to speak.
[0195] A breathing rate could be increased during periods of
increased physical activity or low blood oxygen concentration.
[0196] A breathing rate could be decreased or regularized during
periods of relaxation or sleep. [0197] On-demand breathing
stimulation could be provided in response to the detection of the
onset of irregular breathing during sleep.
[0198] The sensors may be built into the signal generator. For
example, the signal generator may include: [0199] accelerometers
and processor logic configured to determine from outputs of the
accelerometers whether the patient's motions indicate that the
patient is awake or asleep; [0200] an inclinometer or accelerometer
and processor logic configured to determine from one or more
outputs of the inclinometer of accelerometer whether the patient is
lying or upright.
[0201] Other sensors may be implanted. For example, in some
embodiments, a blood chemistry sensor such as a blood oxygen sensor
and/or a blood CO.sub.2 sensor is implanted at a suitable location
in the patient. The blood oxygen monitor may be mounted on an
electrode structure 111 for example. Other sensors may send signals
in the patient's nerves.
[0202] Where a component (e.g. an electrode, signal generator,
lead, stent, assembly, device, antenna, circuit, etc.) is referred
to above, unless otherwise indicated, reference to that component
(including a reference to a "means") should be interpreted as
including as equivalents of that component any component which
performs the function of the described component (i.e., that is
functionally equivalent), including components which are not
structurally equivalent to the disclosed structure which performs
the function in the illustrated exemplary embodiments of the
invention.
[0203] As will be apparent to those skilled in the art in the light
of the foregoing disclosure, many alterations and modifications are
possible in the practice of this invention without departing from
the spirit or scope thereof. For example, electrodes on an
electrode structure may be arranged to provide unipolar, bipolar,
tripolar or balanced tripolar electrode arrangements or
combinations thereof. The example embodiments described herein
include various features such as different geometries for
insulating backing sheets, different arrangements of electrodes,
different control arrangements, and the like. These features may be
mixed and matched (i.e. combined on additional combinations) in
other embodiments of the invention. Accordingly, the scope of the
invention is to be construed in accordance with the substance
defined by the following claims.
* * * * *